Heat-developable light-sensitive materials often contain a base or a base precursor in order to accelerate heat development. Further, it is preferred to use a base precursor releasing a base by thermal decomposition in order to obtain good storage stability of the light-sensitive material.
Typical examples of base precursors are described in British Pat. No. 998,949. A preferred base precursor is a salt of a carboxylic acid and an organic base. Useful carboxylic acids include trichloroacetic acid and trifluoroacetic acid. Useful bases include guanidine, piperidine, morpholine, p-toluidine and 2-picoline. The guanidinetrichloroacetic acid described in U.S. Pat. No. 3,220,846 is particularly useful. Aldoneamides as described in Japanese Patent Application (OPI) No. 22625/75 are decomposed to generate bases at a high temperature and are preferably used.
However, light-sensitive materials containing such base precursors often require a relatively long time to produce an image, or have high fog. Moreover, these base precursors are susceptible to air or moisture, and are subsequently decomposed to change the photographic properties of the light-sensitive material or impair its storability.